MIC2178 Micrel, Inc. MIC2178 2.5A Synchronous Buck Regulator General Description Features The Micrel MIC2178 is a 200kHz synchronous buck (stepdown) switching regulator designed for high-efficiency, battery-powered applications. The MIC2178 operates from a 4.5V to 16.5V input and features internal power MOSFETs that can supply up to 2.5A output current. It can operate with a maximum duty cycle of 100% for use in low-dropout conditions. It also features a shutdown mode that reduces quiescent current to less than 5µA. The MIC2178 achieves high efficiency over a wide output current range by operating in either PWM or skip mode. The operating mode is externally selected, typically by an intelligent system, which chooses the appropriate mode according to operating conditions, efficiency, and noise requirements. The switching frequency is preset to 200kHz and can be synchronized to an external clock signal of up to 300kHz. The MIC2178 uses current-mode control with internal current sensing. Current-mode control provides superior line regulation and makes the regulator control loop easy to compensate. The output is protected with pulse-by-pulse current limiting and thermal shutdown. Undervoltage lockout turns the output off when the input voltage is less than 4.5V. The MIC2178 and is packaged in a 20-lead wide power SOIC package with an operating temperature range of –40°C to +85°C. See the MIC2177 for automatic selection of PWM or skipmode operation. • 4.5V to 16.5V input voltage range • Dual-mode operation for high efficiency (up to 96%) PWM mode for > 200mA load current Skip mode for < 200mA load current • 100mΩ internal power MOSFETs at 12V input • 200kHz preset switching frequency • Low quiescent current 1.0mA in PWM mode 600µA in skip mode < 5µA in shutdown mode • Current-mode control Simplified loop compensation Superior line regulation • 100% duty cycle for low dropout operation • Current limit • Thermal shutdown • Undervoltage lockout Applications • • • • • • • High-efficiency, battery-powered supplies Buck (step-down) dc-to-dc converters Palmtop computers Laptop computers Cellular telephones Hand-held instruments Battery Chargers Typical Application VIN 5.4V to 18V C2 22µF 35V R1 20k ON ENABLE U1 OFF 11 Skip Mode PWM Mode 1,2,9 VIN 20 Ouput Good Output Low 100 10 18 EN MIC2178-5.0 OUT PWRGD SW PGND PWM SYNC COMP SGND R1 10k C3 6.8nF 13 14–17 FB BIAS 10 3,8 4–7 VOUT 5V/2.5A L1, 33µH D1 MBRS140 12 C5 220µF 10V C6 220µF 10V 90 C4 0.01µF R2 10k VIN = 6V 85 80 75 19 5V Output Efficiency 95 EFFICIENCY (%) C1 22µF 35V 70 10 SKIP PWM 100 1000 2500 OUTPUT CURRENT (mA) Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com March 2005 1 M9999-031805 MIC2178 Micrel, Inc. Ordering Information Part Number Standard* Pb-Free Voltage Junction Temp. Package MIC2178BWM MIC2178YWM ADJ –40°C to +85°C 20-lead WSOIC MIC2178-3.3BWM MIC2178-3.3YWM 3.3V –40°C to +85°C 20-lead WSOIC MIC2178-5.0BWM MIC2178-5.0YWM 5.0V –40°C to +85°C 20-lead WSOIC * Standard product will be supported as Pb-Free IAW PPCN #040004 effective 1-1-2005. Pin Configuration VIN 1 20 EN VIN 2 19 BIAS SW 3 18 SYNC PGND 4 17 SGND PGND 5 16 SGND PGND 6 15 SGND PGND 7 14 SGND SW 8 13 COMP VIN 9 12 FB 11 PWRGD PWM 10 20-Lead Wide Power SOIC Pin Description Pin Number Pin Name 1, 2, 9 VIN Supply Voltage (Input): Requires bypass capacitor to PGND. All three pins must be connected to VIN. 3, 8 SW Switch (Output): Internal power MOSFET output switches. Both pins must be externally connected together. 4, 5, 6, 7 PGND Power Ground: Connect all pins to central ground point. 10 PWM PWM/Skip-Mode Control (Input): Logic-level input. Controls regulator operating mode. Logic low enables PWM mode. Logic high enables skip mode. Do not allow pin to float. 11 PWRGD Error Flag (Output): Open-drain output. Active low when FB input is 10% below the reference voltage (VREF). 12 FB 13 COMP Compensation: Output of internal error amplifier. Connect capacitor or series RC network to compensate the regulator control loop. 14, 15, 16, 17 SGND Signal Ground: Connect all pins to ground, PGND*. 18 SYNC Frequency Synchronization (Input): Optional. Connect an external clock signal to synchronize the oscillator. Leading edge of signal above 1.7V terminates switching cycle. Connect to SGND if not used. 19 BIAS Internal 3.3V Bias Supply: Decouple with 0.01µF bypass capacitor to SGND. Do not apply any external load. 20 EN Enable (Input): Logic high enables operation. Logic low shuts down regulator. Do not allow pin to float. M9999-031805 Pin Function Feedback (Input): Connect to output voltage divider resistors. 2 March 2005 MIC2178 Micrel, Inc. Absolute Maximum Ratings Operating Ratings Supply Voltage [100ms transient] (VIN) ......................... 18V Output Switch Voltage (VSW) ........................................ 18V Output Switch Current (ISW) ......................................... 6.0A Enable, PWM Control Voltage (VEN, VPWM) ................. 18V Sync Voltage (VSYNC) ..................................................... 6V Supply Voltage (VIN) ..................................... 4.5V to 16.5V Junction Temperature Range (TJ) ........... –40°C to +125°C Electrical Characteristics VIN = 7.0V; TA = 25°C, bold indicates –40°C ≤ TA ≤ 85°C; unless noted. Symbol Parameter Condition ISS Input Supply Current Min Typ Max Units PWM mode, output not switching, 4.5V ≤ VIN ≤ 16.5V 1.0 1.5 mA skip mode, output not switching, 4.5V ≤ VIN ≤ 16.5V 600 750 µA 1 25 µA VEN = 0V, 4.5V ≤ VIN ≤ 16.5V VBIAS Bias Regulator Output Voltage VIN = 16.5V 3.10 3.30 3.4 V VFB Feedback Voltage MIC2178 [adj.]: VOUT = 3.3V, ILOAD = 0 1.22 1.245 1.27 V VOUT Output Voltage MIC2178 [adj.]: VOUT = 3.3V, 5V ≤ VIN ≤ 16V, 10mA ≤ ILOAD ≤ 2A 3.20 3.14 3.3 3.40 3.46 V V MIC2178-5.0: ILOAD = 0 4.85 5.0 5.15 V MIC2178-5.0: 6V ≤ VIN ≤ 16V, 10mA ≤ ILOAD ≤ 2A 4.85 4.75 5.0 5.15 5.25 V MIC2178-3.3: ILOAD = 0 3.20 3.3 3.40 V MIC2178-3.3: 5V ≤ VIN ≤ 16V, 10mA ≤ ILOAD ≤ 2A 3.20 3.14 3.3 3.40 3.46 V V 4.25 4.35 V VTH Undervoltage Lockout VTL IFB AVOL upper threshold lower threshold Feedback Bias Current 3.90 4.15 MIC2178 [adj.] 60 150 nA MIC2178-5.0, MIC2178-3.3 20 40 µA 20 Error Amplifier Gain 0.6V ≤ VCOMP ≤ 0.8V 15 18 Error Amplifier Output Swing upper limit 0.9 1.5 lower limit Error Amplifier Output Current V source and sink fO Oscillator Frequency DMAX Maximum Duty Cycle VFB = 1.0V tON min Minimum On-Time VFB = 1.5V V 0.05 0.1 V 15 25 35 µA 160 200 240 kHz 100 % 300 SYNC Frequency Range 220 SYNC Threshold 0.8 SYNC Minimum Pulse Width 500 1.6 400 ns 300 kHz 2.2 V ns ISYNC SYNC Leakage VSYNC = 0V to 5.5V –1 0.01 1 µA ILIM Current Limit PWM mode, VIN = 12V 3.8 4.7 5.7 A RON ISW March 2005 Switch On-Resistance Output Switch Leakage skip mode 600 high-side switch, VIN = 12V 90 250 mΩ low-side switch, VIN = 12V 110 250 mΩ 1 10 µA VSW = 16.5V 3 mA M9999-031805 MIC2178 Symbol Micrel, Inc. Parameter Condition Enable Threshold IEN Enable Leakage VEN = 0V to 5.5V PWM Threshold IPWM Min Typ Max Units 0.8 1.6 2.2 V –1 0.01 1 µA 0.6 1.1 1.4 V –1 0.01 1 µA PWM Leakage VPWM = 0V to 5.5V PWRGD Threshold MIC2178 [adj.]: measured at FB pin 1.09 1.13 1.17 V MIC2178-5.0: measured at FB pin 4.33 4.54 4.75 V MIC2178-3.3: measured at FB pin 2.87 3.00 3.13 V PWRGD Output Low ISINK = 1.0mA 0.25 0.4 V PWRGD Off Leakage VPWRGD = 5.5V 0.01 1 µA General Note: Devices are ESD sensitive. Handling precautions recommended. M9999-031805 4 March 2005 MIC2178 Micrel, Inc. Typical Characteristics 180 175 -60 -30 0 30 60 90 120 150 TEMPERATURE (°C) REFERENCE VOLTAGE (V) 1.242 1.240 1.238 -60 -30 0 30 60 90 120 150 TEMPERATURE (°C) Reference Voltage vs. Temperature 5.030 MIC2178-5.0 5.020 5.010 5.000 4.990 4.980 4.970 -60 -30 0 30 60 90 120 150 TEMPERATURE (°C) 18.5 18.0 17.5 17.0 16.5 4.6 4.5 4.4 4.3 4.2 4.1 4 2 0 100 50 2 4 March 2005 4 6 8 10 12 14 16 18 INPUT VOLTAGE (V) 3.285 3.280 -60 -30 0 30 60 90 120 150 TEMPERATURE (°C) Feedback Input Bias Current vs. Temperature 120 90 80 60 40 20 Low-Side Switch On-Resistance 350 125°C 85°C 25°C 0°C 300 250 200 150 100 50 0 3.3V Output Efficiency 2 100 95 VIN = 5V 85 8V 80 12V 75 70 60 10 100 0 -60 -30 0 30 60 90 120 150 TEMPERATURE (°C) 6 8 10 12 14 16 18 INPUT VOLTAGE (V) SKIP PWM 65 2 3.290 95 EFFICIENCY (%) SUPPLY CURRENT (mA) 6 150 100 OUTPUT SWITCHING 8 125°C 85°C 25°C 0°C 200 0 PWM-Mode Supply Current 10 3.295 High-Side Switch On-Resistance 250 4.0 -60 -30 0 30 60 90 120 150 TEMPERATURE (°C) 12 3.300 16.0 -60 -30 0 30 60 90 120 150 TEMPERATURE (°C) ON-RESISTANCE (mΩ) 4.8 4.7 3.305 Error-Amplifier Gain vs. Temperature 19.0 Current Limit vs. Temperature 5.0 4.9 CURRENT LIMIT (A) 1.244 3.310 BIAS CURRENT (nA) 185 1.246 MIC2178-3.3 3.315 ON-RESISTANCE (mΩ) 190 1.248 Reference Voltage vs. Temperature 3.320 100 1000 2500 OUTPUT CURRENT (mA) 5 EFFICIENCY (%) 195 MIC2178 [adj.] 1.250 AMPLIFIER VOLTAGE GAIN FREQUENCY (kHz) 200 Reference Voltage vs. Temperature 1.252 REFERENCE VOLTAGE (V) 205 REFERENCE VOLTAGE (V) Oscillator Frequency vs. Temperature 4 6 8 10 12 14 16 18 INPUT VOLTAGE (V) 5V Output Efficiency VIN = 6V 90 8V 85 12V 80 75 70 10 SKIP PWM 100 1000 2500 OUTPUT CURRENT (mA) M9999-031805 MIC2178 Micrel, Inc. Block Diagram VIN 4.5V to 16.5V 100µF VIN UVLO, Thermal Shutdown EN Enable Shutdown 20 1 2 9 100mΩ P-channel 3.3V Regulator L 3 D 100mΩ N-channel 19 0.01µF VOUT COUT PGND 4 internal supply Voltage PWM Skip Mode PWM Mode 10 5 ILIMIT Comp. SYNC 18 * 6 * Connect SGND to PGND 7 PWM/ Skip-Mode Select ILIMIT Thresh. Voltage Bold lines indicate high current traces Corrective Ramp Stop 1 8 BIAS 10k R1 R2 1.245 SW ISENSE Amp. Output Control Logic VOUT 200kHz Oscillator R1 Skip-Mode Comp. Reset Pulse FB R 12 Q S VIN Power Good Comp. PWM Comp. R2 20k PWRGD Output Good 11 RC COMP 13 CC 1.13V VREF 1.245V MIC2178 [Adjustable] SGND M9999-031805 14 6 15 16 17 March 2005 MIC2178 Micrel, Inc. connect an external load to the BIAS pin. It is not designed to provide an external supply voltage. Frequency Synchronization The MIC2178 operates at a preset switching frequency of 200kHz. It can be synchronized to a higher frequency by connecting an external clock to the SYNC pin. The SYNC pin is a logic level input that synchronizes the oscillator to the rising edge of an external clock signal. It has a frequency range of 220kHz–300kHz, and can operate with a minimum pulse width of 500ns. If synchronization is not required, connect SYNC to ground. Power Good Flag The power good flag (PWRGD) is an error flag that alerts a system when the output is not in regulation. When the output voltage is 10% below its nominal value, PWRGD is logic low, signaling that VOUT is to low. PWRGD is an open-drain output that can sink 1mA from a pull-up resistor connected to VIN. Low-Dropout Operation Output regulation is maintained in PWM or skip mode even when the difference between VIN and VOUT decreases below 1V. As VIN – VOUT decreases, the duty cycle increases until it reaches 100%. At this point, the P-channel is kept on for several cycles at a time, and the output stays in regulation until VIN – VOUT falls below the dropout voltage (dropout voltage = P-channel on-resistance × load current). PWM-Mode Operation Refer to “PWM Mode Functional Diagram” which is a simplified block diagram of the MIC2178 operating in PWM mode and its associated waveforms. When operating in PWM mode, the output P-channel and Nchannel MOSFETs are alternately switched on at a constant frequency and variable duty cycle. A switching period begins when the oscillator generates a reset pulse. This pulse resets the RS latch which turns on the P-channel and turns off the N-channel. During this time, inductor current (IL1) increases and energy is stored in the inductor. The current sense amplifier (ISENSE Amp) measures the P-channel drain-tosource voltage and outputs a voltage proportional to IL1. The output of ISENSE Amp is added to a sawtooth waveform (corrective ramp) generated by the oscillator, creating a composite waveform labeled ISENSE on the timing diagram. When ISENSE is greater than the error amplifier output, the PWM comparator will set the RS latch which turns off the Pchannel and turns on the N-channel. Energy is then discharged from the inductor and IL1 decreases until the next switching cycle begins. By varying the P-channel on-time (duty cycle), the average inductor current is adjusted to whatever value is required to regulate the output voltage. The MIC2178 uses current-mode control to adjust the duty cycle and regulate the output voltage. Current-mode control has two signal loops that determine the duty cycle. One is an outer loop that senses the output voltage, and the other is a faster inner loop that senses the inductor current. Signals from these two loops control the duty cycle in the following way: VOUT is fed back to the error amplifier which compares the feedback voltage (VFB) to an internal reference voltage Functional Description Micrel’s MIC2178 is a synchronous buck regulator that operates from an input voltage of 4.5V to 16.5V and provides a regulated output voltage of 1.25V to 16.5V. Its has internal power MOSFETs that supply up to 2.5A load current and operates with up to 100% duty cycle to allow low-dropout operation. To optimize efficiency, the MIC2178 operates in PWM and skip mode. Skip mode provides the best efficiency when load current is less than 200mA, while PWM mode is more efficient at higher current. PWM or skip-mode operation is selected externally, allowing an intelligent system (i.e. microprocessor controlled) to select the correct operating mode for efficiency and noise requirements. During PWM operation, the MIC2178 uses current-mode control which provides superior line regulation and makes the control loop easier to compensate. The PWM switching frequency is set internally to 200kHz and can be synchronized to an external clock frequency up to 300kHz. Other features include a low-current shutdown mode, current limit, undervoltage lockout, and thermal shutdown. See the following sections for more detail. Switch Output The switch output (SW) is a half H-bridge consisting of a highside P-channel and low-side N-channel power MOSFET. These MOSFETs have a typical on-resistance of 100mΩ when the MIC2178 operates from a 12V supply. Antishootthrough circuitry prevents the P-channel and N-channel from turning on at the same time. Current Limit The MIC2178 uses pulse-by-pulse current limiting to protect the output. During each switching period, a current limit comparator detects if the P-Channel current exceeds 4.7A. When it does, the P-channel is turned off until the next switching period begins. Undervoltage Lockout Undervoltage lockout (UVLO) turns off the output when the input voltage (VIN) is to low to provide sufficient gate drive for the output MOSFETs. It prevents the output from turning on until VIN exceeds 4.3V. Once operating, the output will not shut off until VIN drops below 4.2V. Thermal Shutdown Thermal shutdown turns off the output when the MIC2178 junction temperature exceeds the maximum value for safe operation. After thermal shutdown occurs, the output will not turn on until the junction temperature drops approximately 10°C. Shutdown Mode The MIC2178 has a low-current shutdown mode that is controlled by the enable input (EN). When a logic 0 is applied to EN, the MIC2178 is in shutdown mode, and its quiescent current drops to less than 5µA. Internal Bias Regulator An internal 3.3V regulator provides power to the MIC2178 control circuits. This internal supply is brought out to the BIAS pin for bypassing by an external 0.01µF capacitor. Do not March 2005 7 M9999-031805 MIC2178 Micrel, Inc. (VREF). When VOUT is lower than its nominal value, the error amplifier output voltage increases. This voltage then intersects the current sense waveform later in switching period which increases the duty cycle and the average inductor current . If VOUT is higher than nominal, the error amplifier output voltage decreases, reducing the duty cycle. The PWM control loop is stabilized in two ways. First, the inner signal loop is compensated by adding a corrective ramp to the output of the current sense amplifier. This allows the regulator to remain stable when operating at greater than 50% duty cycle. Second, a series resistor-capacitor load is connected to the error amplifier output (COMP pin). This places a pole-zero pair in the regulator control loop. One more important item is synchronous rectification. As mentioned earlier, the N-channel output MOSFET is turned on after the P-channel turns off. When the N-channel turns on, its on-resistance is low enough to create a short across the output diode. As a result, inductor current flows through the N-channel and the voltage drop across it is significantly lower than a diode forward voltage. This reduces power dissipation and improves efficiency to greater than 95% under certain operating conditions. To prevent shoot through current, the output stage employs break-before-make circuitry that provides approximately 50ns of delay from the time one MOSFET turns off and the other turns on. As a result, inductor current briefly flows through the output diode during this transition. Skip-Mode Operation Refer to “Skip Mode Functional Diagram” which is a simplified block diagram of the MIC2178 operating in skip mode and its associated waveforms. Skip-mode operation turns on the output P-channel at a frequency and duty cycle that is a function of VIN, VOUT, and the output inductor value. While in skip mode, the N-channel is kept off to optimize efficiency by reducing gate charge dissipation. VOUT is regulated by skipping switching cycles that turn on the P-channel. To begin analyzing MIC2178 skip mode operation, assume the skip-mode comparator output is high and the latch output has been reset to a logic 1. This turns on the P-channel and causes IL1 to increase linearly until it reaches a current limit of 600mA. When IL1 reaches this value, the current limit comparator sets the RS latch output to logic 0, turning off the M9999-031805 P-channel. The output switch voltage (VSW) then swings from VIN to 0.4V below ground, and IL1 flows through the Schottky diode. L1 discharges its energy to the output and IL1 decreases to zero. When IL1 = 0, VSW swings from –0.4V to VOUT, and this triggers a one-shot that resets the RS latch. Resetting the RS latch turns on the P-channel, and this begins another switching cycle. The skip-mode comparator regulates VOUT by controlling when the MIC2178 skips cycles. It compares VFB to VREF and has 10mV of hysteresis to prevent oscillations in the control loop. When VFB is less than VREF –5mV, the comparator output is logic 1, allowing the P-channel to turn on. Conversely, when VFB is greater than VREF + 5mV, the P-channel is turned off. Note that this is a self oscillating topology which explains why the switching frequency and duty cycle are a function of VIN, VOUT, and the value of L1. It has the unique feature (for a pulse-skipping regulator) of supplying the same value of maximum load current for any value of VIN, VOUT, or L1. This allows the MIC2178 to always supply up to 300mA of load current when operating in skip mode. Selecting PWM- or Skip-Mode Operation PWM or skip mode operation is selected by an external logic signal applied to the PWM pin. A logic low places the MIC2178 into PWM mode, and logic high places it into skip mode. Skip mode operation provides the best efficiency when load current is less than 200mA, and PWM operation is more efficient at higher currents. The MIC2178 was designed to be used in intelligent systems that determine when it should operate in PWM or skip mode. This makes the MIC2178 ideal for applications where a regulator must guarantee low noise operation when supplying light load currents, such as cellular telephone, audio, and multimedia circuits. There are two important items to be aware of when selecting PWM or skip mode. First, the MIC2178 can start-up only in PWM mode, and therefore requires a logic low at PWM during start-up. Second, in skip mode, the MIC2178 will supply a maximum load current of approximately 300mA, so the output will drop out of regulation when load current exceeds this limit. To prevent this from occurring, the MIC2178 should change from skip to PWM mode when load current exceeds 200mA. 8 March 2005 MIC2178 Micrel, Inc. PWM-Mode Functional Diagram VIN 4.5V to 16.5V CIN VIN 1 2 9 100mΩ P-channel VOUT 1.245 R1 R2 1 SW ISENSE Amp. L1 3 VOUT 8 IL1 D 100mΩ N-channel COUT PGND 4 5 6 7 Corrective Ramp Stop SYNC 18 200kHz Oscillator R1 Reset Pulse FB 12 R2 R Q S PWM Comp. Error Amp. COMP CC RC 13 VREF 1.245V MIC2178 [Adjustable] PWM-Mode Signal Path SGND 14 15 16 17 VSW Reset Pulse IL1 ILOAD ∆IL1 Error Amp. Output ISENSE March 2005 9 M9999-031805 MIC2178 Micrel, Inc. Skip-Mode Functional Diagram VIN 4.5V to 16.5V CIN VIN 1 2 9 Output Control Logic S Q 100mΩ P-channel R One Shot ISENSE Amp. VOUT 1.245 R1 R2 1 SW L1 3 VOUT 8 IL1 D COUT PGND 4 5 ILIMIT Comp. 6 7 ILIMIT Thresh. Voltage R1 Skip-Mode Comp. FB 12 R2 VREF 1.245V MIC2178 [Adjustable] Skip-Mode Signal Path SGND VSW 14 15 16 17 VIN VOUT 0 One-Shot Pulse ILIM IL1 0 VREF + 5mV VFB VREF – 5mV M9999-031805 10 March 2005 MIC2178 Micrel, Inc. To maximize efficiency, the inductor’s resistance must be less than the output switch on-resistance (preferably, 50mΩ or less). Output Capacitor Selection Select an output capacitor that has a low value of ESR. This parameter determines a regulator’s output ripple voltage (VRIPPLE) which is generated by ∆IL x ESR. Therefore, ESR must be equal or less than a maximum value calculated for a specified VRIPPLE (typically less than 1% of the output voltage) and ∆IL(max): Application Information Feedback Resistor Selection (Adjustable Version) The output voltage is programmed by connecting an external resistive divider to the FB pin as shown in “MIC2178 Block Diagram.” The ratio of R1 to R2 determines the output voltage. To optimize efficiency during low output current operation, R2 should not be less than 20kΩ. However, to prevent feedback error due to input bias current at the FB pin, R2 should not be greater than 100kΩ. After selecting R2, calculate R1 with the following formula: V R1 = R2 OUT – 1 1.245V ESRMAX = Typically, capacitors in the range of 100 to 220µF have ESR less than this maximum value. The output capacitor can be a low ESR electrolytic or tantalum capacitor, but tantalum is a better choice for compact layout and operation at temperatures below 0°C. The voltage rating of a tantalum capacitor must be 2 × VOUT, and the voltage rating of an electrolytic must be 1.4 × VOUT. Output Diode Selection In PWM operation, inductor current flows through the output diode approximately 50ns during the dead time when one output MOSFET turns off the other turns on. In skip mode, the inductor current flows through the diode during the entire Pchannel off time. The correct diode for both of these conditions is a 1A diode with a reverse voltage rating greater than VIN. It must be a Schottky or ultrafast-recovery diode (tR < 100ns) to minimize power dissipation from the diode’s reverse-recovery charge. Compensation Compensation is provided by connecting a series RC load to the COMP pin. This creates a pole-zero pair in the regulator control loop, allowing the regulator to remain stable with enough low frequency loop-gain for good load and line regulation. At higher frequencies, the pole-zero reduces loop-gain to a level referred to as the mid-band gain. The midband gain is low enough so that the loop gain crosses 0db with sufficient phase margin. Typical values for the RC load are 4.7nF to 10nF for the capacitor and 5kΩ to 20kΩ for the resistor. Printed Circuit Board Layout A well designed PC board will prevent switching noise and ground bounce from interfering with the operation of the MIC2178. A good design takes into consideration component placement and routing of power traces. The first thing to consider is the locations of the input capacitor, inductor, output diode, and output capacitor. The input capacitor must be placed very close to the VIN pin, the inductor and output diode very close to the SW pin, and the output capacitor near the inductor. These components pass large high-frequency current pulses, so they must use short, wide power traces. In addition, their ground pins and PGND are connected to a ground plane that is nearest the power supply ground bus. Input Capacitor Selection The input capacitor is selected for its RMS current and voltage rating and should be a low ESR (equivalent series resistance) electrolytic or tantalum capacitor. As a rule of thumb, the voltage rating for a tantalum capacitor should be twice the value of VIN, and the voltage rating for an electrolytic should be 40% higher than VIN. The RMS current rating must be equal or greater than the maximum RMS input ripple current. A simple, worst case formula for calculating this RMS current is: IRMS(max) = ILOAD(max) 2 Tantalum capacitors are a better choice for applications that require the most compact layout or operation below 0°C. The input capacitor must be located very close to the VIN pin (within 0.2in, 5mm). Also, place a 0.1µF ceramic bypass capacitor as close as possible to VIN. Inductor Selection The MIC2178 is a current-mode controller with internal slope compensation. As a result, the inductor must be at least a minimum value to prevent subharmonic oscillations. This minimum value is calculated by the following formula: LMIN = VOUT × 3.0µH/V In general, a value at least 20% greater than LMIN should be selected because inductor values have a tolerance of ±20%. Two other parameters to consider in selecting an inductor are winding resistance and peak current rating. The inductor must have a peak current rating equal or greater than the peak inductor current. Otherwise, the inductor may saturate, causing excessive current in the output switch. Also, the inductor’s core loss may increase significantly. Both of these effects will degrade efficiency. The formula for peak inductor current is: IL(peak) = ILOAD(max) + ∆IL(max) 2 Where: VOUT 5µs ∆IL(max) = VOUT 1 − × V L IN(max) March 2005 VRIPPLE ∆IL(max) 11 M9999-031805 MIC2178 Micrel, Inc. The feedback resistors, RC compensation network, and BIAS pin bypass capacitor should be located close to their respective pins. To prevent ground bounce, their ground traces and SGND should not be in the path of switching currents returning to the power supply ground bus. SGND and PGND should be tied together by a ground plane that extends under the MIC2178. VIN 4.5V to 16.5V C1 22µF 35V R1 20k U1 1,2,9 L1 50µH VIN 20 11 Skip Mode PWM Mode 10 18 EN 3,8 SW PWRGD MIC2178 PGND PWM SYNC COMP SGND 13 R2 10k 4–7 12 FB BIAS 14–17 19 C3 0.01µF C4 6.8nF VOUT 3.3V/1A C2 100µF 10V D1 MBRS130L R3 10k U1 C1 C2 C3 C4 D1 L1 L1 L1 Micrel AVX AVX Z5UorX7R X7RorNP0 Motorola Coiltronics Coilcraft Bi MIC2178-3.3BWM TPSE226M035R0300, ESR = 0.3Ω TPSD107M010R0100, ESR = 0.1Ω Ceramic Dielectric Material Ceramic Dielectric Material MBRS130LT3 CTX50-4P, DCR = 0.097 Ω DO3316P-473, DCR = 0.12Ω HM77-11003, DCR = 0.073Ω Figure 1. MIC2178 4.5V–16.5V to 3.3V/1A Regulator VIN 5.4V to 16.5V C1 22µF 35V R1 20k U1 20 11 Skip Mode PWM Mode 1,2,9 L1 50µH VIN 10 18 EN SW PWRGD MIC2178 PGND PWM SYNC COMP SGND 13 R2 10k C4 6.8nF 14–17 FB 3,8 VOUT 5V/1A C2 100µF 10V D1 MBRS130L 4–7 12 BIAS 19 C3 0.01µF R3 10k U1 C1 C2 C3 C4 D1 L1 L1 L1 Micrel AVX AVX Z5UorX7R X7RorNP0 Motorola Coiltronics Coilcraft Bi MIC2178-5.0BWM TPSE226M035R0300, ESR = 0.3Ω TPSD107M010R0100, ESR = 0.1Ω Ceramic Dielectric Material Ceramic Dielectric Material MBRS130LT3 CTX50-4P, DCR = 0.097 Ω DO3316P-473, DCR = 0.12Ω HM77-11003, DCR = 0.073Ω Figure 2. MIC2178 5.4V–16.5V to 5V/1A Regulator M9999-031805 12 March 2005 MIC2178 Micrel, Inc. VIN 12.5V to 16.5V C1 22µF 35V R1 20k U1 1,2,9 L1 68µH VIN 20 EN 11 Skip Mode PWM Mode SW PWRGD MIC2178 PGND PWM 10 18 FB SYNC COMP SGND 13 3,8 VOUT 12V/1A D1 MBRS130L 4–7 R2 174k 1% 12 U1 Micrel MIC2178BWM C1 AVX TPSE226M035R0300, ESR = 0.3Ω TPSE686M020R0150, ESR = 0.15Ω R1 C2 AVX 20k C3 Z5UorX7R Ceramic Dielectric Material C4 X7RorNP0 Ceramic Dielectric Material 1% D1 Motorola MBRS130LT3 L1 Coiltronics CTX68-4P, DCR = 0.238 Ω L1 Coilcraft DO3316P-683, DCR = 0.016Ω L1 Bi HM77-11003, DCR = 0.233Ω BIAS 14–17 19 R2 10k C3 0.01µF C4 6.8nF C2 68µF 20V R3 10k Figure 3. MIC2178 12.5V–16.5V to 12V/1A Regulator VIN 10V to 16.5V C1 22µF 35V X2 R1 20k U1 1,2,9 L1 33µH VIN 20 11 Skip Mode PWM Mode 10 18 EN SW PWRGD MIC2178 PGND PWM FB SYNC COMP SGND 13 3,8 4–7 19 R2 10k C3 0.01µF C4 6.8nF C2 220µF 10V X2 12 BIAS 14–17 VOUT 3.3V/2.5A D1 MBRS130L R3 10k U1 C1 C2 C3 C4 D1 L1 Micrel AVX AVX Z5UorX7R X7RorNP0 Motorola Bi MIC2178-3.3BWM TPSE226M035R0300, ESR = 0.3Ω TPSE227M010R0100, ESR = 0.1Ω Ceramic Dielectric Material Ceramic Dielectric Material MBRS130LT3 HM77-18004, DCR = 0.075Ω Figure 4. MIC2178 10V–16.5V to 3.3V/2.5A Regulator VIN 4.5V to 10V C1 22µF 35V R1 20k U1 20 11 Skip Mode PWM Mode 1,2,9 L1 33µH VIN 10 18 EN SW PWRGD MIC2178 PGND PWM SYNC COMP SGND 13 R2 10k C4 6.8nF 14–17 FB 3,8 VOUT 3.3V/1A D1 MBRS130L 4–7 C2 100µF 10V 12 BIAS 19 C3 0.01µF R3 10k U1 C1 C2 C3 C4 D1 L1 L1 L1 Micrel AVX AVX Z5UorX7R X7RorNP0 Motorola Coiltronics Coilcraft Bi MIC2178-3.3BWM TPSE226M035R0300, ESR = 0.3Ω TPSD107M010R0100, ESR = 0.1Ω Ceramic Dielectric Material Ceramic Dielectric Material MBRS130LT3 CTX33-3P, DCR = 0.077 Ω DO3316-333, DCR = 0.088Ω HM77-60002, DCR = 0.035Ω Figure 5. MIC2178 4.5V–10V to 3.3V/1A Regulator March 2005 13 M9999-031805 MIC2178 Micrel, Inc. Q1 SI9435 VIN D S 4.5V to 16.5V G C1 22µF 35V R1 20k U1 1,2,9 L1 50µH VIN 20 11 Skip Mode PWM Mode 10 18 EN SW PWRGD MIC2178 PGND PWM SYNC COMP SGND 13 FB 3,8 4–7 14–17 19 C3 0.01µF C4 6.8nF C2 100µF 10V 12 BIAS R2 10k VOUT 3.3V/1A D1 MBRS130L C3 0.01µF U1 C1 C2 C3 C4 D1 Q1 L1 L1 L1 Micrel AVX AVX Z5UorX7R X7RorNP0 Motorola Siliconix Coiltronics Coilcraft Bi MIC2178-3.3BWM TPSE226M035R0300, ESR = 0.3Ω TPSD107M010R0100, ESR = 0.1Ω Ceramic Dielectric Material Ceramic Dielectric Material MBRS130LT3 Si9435DY PMOS CTX50-4P, DCR = 0.097 Ω DO3316-473, DCR = 0.12Ω HM77-11003, DCR = 0.073Ω Figure 6. MIC2178 Reversed Battery Protected Regulator VIN 8V to 16.5V C1 22µF 35V R1 20k U1 20 11 Skip Mode PWM Mode 1,2,9 T1 50µH VIN 10 18 EN SW PWRGD MIC2178 PGND 4–7 2 D1 MBRS130L SYNC COMP SGND 14–17 FB C2 100µF 10V 12 BIAS C4 100µF 10V 19 R2 10k C6 6.8nF C5 0.01µF R3 10k 4 3 Micrel AVX AVX AVX AVX Z5UorX7R X7RorNP0 Motorola Motorola Coiltronics 1 PWM 13 U1 C1 C2 C3 C4 C5 C6 D1 D2 L1 +VOUT/+IOUT 5V/0.5A 3,8 MIC2178-5.0BWM TPSE226M035R0300, ESR = 0.3Ω TPSD107M010R0100, ESR = 0.1Ω TPSD107M010R0100, ESR = 0.1Ω TPSD107M010R0100, ESR = 0.1Ω Ceramic Dielectric Material Ceramic Dielectric Material MBRS130LT3 MBRS130LT3 CTX50-4P, DCR = 0.097 Ω C2 100µF 10V D2 MBRS130L +IOUT + (–IOUT ) 1A VOUT DC = + VIN DC 40% then – IOUT + IOUT DC + IOUT 40% then – IOUT –VOUT/-IOUT –5V/0.5A (1– DC) Figure 7. MIC2178 8V–16.5V to ±5V/500mA Regulator M9999-031805 14 March 2005 MIC2178 Micrel, Inc. Suggested Manufacturers List Inductors Capacitors Diodes Transistors Coilcraft 1102 Silver Lake Rd. Cary, IL 60013 tel: (708) 639-2361 fax: (708) 639-1469 AVX Corp. 801 17th Ave. South Myrtle Beach, SC 29577 tel: (803) 448-9411 fax: (803) 448-1943 General Instruments (GI) 10 Melville Park Rd. Melville, NY 11747 tel: (516) 847-3222 fax: (516) 847-3150 Siliconix 2201 Laurelwood Rd. Santa Clara, CA 96056 tel: (800) 554-5565 Coiltronics 6000 Park of Commerce Blvd. Boca Raton, FL 33487 tel: (407) 241-7876 fax: (407) 241-9339 Sanyo Video Components Corp. 2001 Sanyo Ave. San Diego, CA 92173 tel: (619) 661-6835 fax: (619) 661-1055 International Rectifier Corp. 233 Kansas St. El Segundo, CA 90245 tel: (310) 322-3331 fax: (310) 322-3332 Bi Technologies 4200 Bonita Place Fullerton, CA tel: (714) 447-2345 fax: (714) 447-2500 Sprague Electric Lower Main St. 60005 Sanford, ME 04073 tel: (207) 324-4140 Motorola Inc. MS 56-126 3102 North 56th St. Phoenix, AZ 85018 tel: (602) 244-3576 fax: (602) 244-4015 Package Information PIN 1 DIMENSIONS: INCHES (MM) 0.301 (7.645) 0.297 (7.544) 0.027 (0.686) 0.031 (0.787) 0.050 (1.270) TYP 0.094 (2.388) 0.090 (2.286) 0.016 (0.046) TYP 0.509 (12.929) 0.505 (12.827) 0.103 (2.616) 0.099 (2.515) 7° TYP 0.015 R (0.381) 0.015 (0.381) SEATING MIN PLANE 0.297 (7.544) 0.293 (7.442) 0.330 (8.382) 0.326 (8.280) 0.022 (0.559) 0.018 (0.457) 5° TYP 10° TYP 0.032 (0.813) TYP 0.408 (10.363) 0.404 (10.262) 20-Lead Wide SOP (WM) MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2001 Micrel Incorporated March 2005 15 M9999-031805